This invention relates generally to feed rolls for logs or other similar elongated objects. More particularly it relates to an improved feed roll having upstanding "spikes" affixed to the generally cylindrical surface.
Feed rolls for logs are used in various log handling applications such as feeding unbarked logs through a debarker, feeding logs through a sawing machine, and for feeding trees through a delimber. Each of these exemplary applications has different requirements with respect to the feed characteristics of the log and of the feed rolls. Two basic requirements are that the feed rolls provide sufficient motive force to carry the logs through the processing station and that they be transported through the rolls without undue damage to the log or tree.
One of the applications requiring a significant motive force in view of the reaction forces created by the process is the delimber. In order to provide the motive force traction must be developed between the feed roll and the log surface. Typically spikes extending radially outwardly from the surface of the feed roll would act to clutch the log surface and motivate it. With significant reaction forces created by the delimber knives, the spikes are required to penetrate the surface of the log causing damage. Such damage reduces the value of the log based upon the fact that fewer and/or lower value products are produced. As the logs become generally smaller in diameter, the problem of surface damage becomes even more significant.
In a typical delimbing application a pair of spiked feed rolls will act in unison to pull a log through a set of delimbing knives. Each roll can be driven by a gear and pinion arrangement that is housed in a case which pivots about the pinion shaft. This structure, as will be well understood by those skilled in the art, allows the rolls to move laterally to adjust to the tree diameter. A suitable cross linkage provides simultaneous lateral motion and a hydraulic cylinder provides the opening and closing action allowing the rolls to continuously follow the surface of the tree. To develop the necessary traction the spikes will penetrate the surface.
The significant forces involved in the delimbing application are the feed force acting parallel to the tree and a normal force forcing the feed roll spikes into the surface to generate the traction necessary to transmit the feed force. The normal force has several components. These forces acting through the spikes develop the required traction to overcome the reaction force from the knives and bring the trees through the knives at an adequate production rate.
In the past the typical spike configuration used has been conical. Rows of conical spikes are spaced about the circumference of the roll and are siged and spaced to provide the best available feeding characteristics with the least amount of damage. Another typical configuration is the saw tooth where circumferentially spaced rows of saw tooth bars are afixed to the roll surface.
It has been found that the typical conically spiked roll could be improved and that certain configurations afford improved traction with less wood damage. Not only does the improvement afford better traction and less damage, but it also is of simple construction and lends itself to easy maintenance.
Briefly, the present invention is practiced in one form by a feed roll having a plurality of trapenzoidally shaped pyramids spaced about the circumference of the roll. In adjacent rows of trapezoidal pyramids an offset is maintained. Certain dimensional characteristics are provided to yield the increased traction with reduced damage.